1. Field of the Invention
This invention relates to position control systems and, in particular, to systems for use in selectively positioning a movable member of an operator-positionable machine tool to preselected positions.
2. Description of the Prior Art
In the positioning of movable members, such as machine tool beds, encoding devices provide an accurate indication of the X and Y coordinates of the position of the movable member. One such encoding device includes a transducer that responds to the movement of an actuator mounted for movement with the machine tool bed.
Such encoders have been coupled to a digital readout counter to display position information with respect to a reference coordinate or reference position. The operator may control the bed-moving mechanism of the machine tool under the guidance of the display so that the display indicates when the position of the bed corresponds to the desired positions. When moving from point to point, the operator must compare the present position of the machine tool bed to the next desired position as defined by the blueprint. The operator must then guide the movable member to that next desired position and recheck the blueprint to determine that the machine tool bed is in the desired position. This is cumbersome and often results in error.
Another device manufactured by Anilam Electronics Corp. of Miami, Fla., employs a similar encoder, but displays a zero indication each time the operator reaches the successive desired positions. This device is considered to be an improvement of the device discussed above. Unfortunately, however, this device requires that the operator individually increment the preceding X and Y coordinates to define the next desired position when entering the plurality of selected points in the device when programming it. The coordinate information on blueprints or charts is usually defined from a common reference point rather than X and Y incremental additions to preceding points. Thus, when entering the data into this device, the operator must make successive calculations of the difference between the X and Y coordinates of successive points.